1. Field of The Invention
The present invention relates to a control circuit of a direct current servomotor for a floppy disk drive, and more particularly to a control circuit which improves starting capability for initial rotation of a floppy disk.
Furthermore, the present invention also relates to a control system of a spindle motor for a floppy disk drive which drives and rotates a magnetic disk by means of engaging a drive pin with a drive hole of the magnetic disk, and more particularly to a motor control system which is improved to obtain initial large start-up torque.
2. Description of The Prior Art
It is well-known that there is a floppy disk drive which drives and rotates the floppy disk that magnetic recording medium is coated on the surface of deflectable plastic thin film and which performs read/write operation of information at a requested track position by means of traveling read/write heads toward the radial direction of the floppy disk. The floppy disk drive is of wide use as an external data storage device for computors.
In recent years, this kind of floppy disk drive has been not only requested to be designed its total system with a low cost, small sizes and a little consumption of electric power, but also to increase its initial start-up torque without any increased cost, large sizes nor much consumption of electric power.
In the ordinary cases, a spindle motor consisting of direct current servomotor drives and rotates the floppy disk with a constant rotating speed, and in order to make an initial start-up of the floppy disk drive firmly the spindle motor is required sufficient torque at the start-up of the disk. The start-up operation is performed in such a state that a drive pin mounted on the shaft of the spindle motor is engaged with a drive hole provided in the hub fixed on the central portion of the magnetic disk and the shaft of the spindle motor and the hub of the magnetic disk are firmly chucked together. The spindle motor is required large start-up torque for overcoming the disk rotating load at the start-up of the spindle motor.
In order to increase the start-up torque of the motor, strong rotor magnet or increase of electric current and the number of turns in the drive coil must be considered, but these cause in volume of the motor, increase of cost or increase of electric power consumption.